Fluid-operated braking systems such as air brake systems have long been used to control the movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles, such as trucks which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel require a braking system which responds rapidly with substantial braking power. One system component which is instrumental in the operation of air brake systems is the brake actuator. The brake actuator provides the force necessary when braking a vehicle.
Commercial air brake actuators can actuate the normal surface brakes as well as parking/emergency brakes. The brake actuators, also known as spring brakes, typically have a network of air chambers defined by one or more diaphragms and/or pistons and a plurality of springs which operate to provide the appropriate braking action in response to inputs by the vehicle driver. In the event an air braking system loses pressure, the brake actuator automatically engages the vehicle brakes.
In brake actuators of this type, the diaphragms are typically flexible, cup-shaped and have an outer radial rim which is received and compressed between flange portions of a housing and cover. Such diaphragms are generally formed of a rubber material with a fibrous reinforcement disposed therein. U.S. Pat. Nos. 3,842,716, 3,872,777, 5,115,719, 6,131,501 and 6,212,996 each disclose examples of diaphragms for use in brake actuators having various configurations.
One problem with diaphragm-type brake actuators is that an adequate seal must be provided at an outer peripheral surface of the diaphragm, which is squeezed between the housings. This seal has sometimes been somewhat difficult to obtain since the diaphragm may be positioned off center between the housings during assembly. Thus, should the diaphragm be positioned off center when the housings are secured together, an adequate seal may not be provided. Numerous attempts have been made to obviate this problem. For example, U.S. Pat. No. 5,992,297 discloses a diaphragm having an outer wedge-shaped edge portion with flats adjacent thereto. The flats are supposed to help facilitate assembly of the brake actuator. U.S. Pat. Nos. 5,765,466 and 5,507,217 disclose diaphragms which have particular configurations about their peripheries. These configurations are supposed to facilitate centering and aid in maintaining proper alignment during assembly.
Another problem associated with diaphragm-type brake actuators is that after repeated use, the diaphragms may tend to pull out of the mechanically clamped sealing area of the actuator assembly, thereby causing leakage and possibly rendering the brake actuator inoperative. As this phenomenon can occur even if the diaphragm was properly aligned and seated during assembly, the above-referenced patents do not adequately address this problem.
U.S. Pat. No. 3,911,796 discloses a diaphragm having a plurality of protuberances thereon which are supposed to help the diaphragm resist abrasion and wear, and thus inhibit leaks from being created. However, this patent discloses no design which would adequately help prevent the diaphragm from pulling out of its sealing area.
What is desired, therefore, is a diaphragm-type brake actuator which is not prone to leaking or developing leaks and which incorporates a diaphragm which resists pull out from its sealing area even after extended use.